Cognitive Neuroscience. Questions. Multiple Methods. Electrophysiology. Multiple Methods. Approaches to Thinking about the Mind

Transcription

1 Cognitive Neuroscience Approaches to Thinking about the Mind Cognitive Neuroscience Evolutionary Approach Sept 20-22, 2004 Interdisciplinary approach Rapidly changing How does the brain enable cognition? The relation between brain structure, brain function, and cognitive function Questions Can we learn about cognition from studying the brain? Is it necessary to study the brain to study cognition? Multiple Methods Each method has advantages and limitations Think about if you had to choose only one method Cognitive (information processing) Human Lesion ERP fmri Multiple Methods Electrophysiology What are assumptions, advantages, and limitations? 1

2 Single-cell recording Advantages and Limitations? Advantages and Limitations? Record single neuron activity in awake animal May be difficult to determine which part of task is associated with neuron Cannot be used with humans EEG and ERP EEG and ERP Measure of summed electrical potential Detect general level of brain activity 2

3 Advantages and Limitations Precise temporal record Non-invasive Early sensory components can be modulated by attention Coarse info about localization Inverse problem May not apply to longer cognitive processes Large number of trials needed MEG Magnetoencephalography Measures small magnetic fields associated with synaptic activity Advantage in localization because magnetic fields are not distorted as they pass through brain, skull, scalp Dipole modeling more accurate Penfield Electrical Stimulation 3

4 Electrical Stimulation Brain Lesions Humans Animals Assumption If damage to a region of the brain results in an inability to perform a specific function, then the function was supported by that particular brain region Focus on dissociations or modularity As in cognitive approach Single Dissociation Tasks A and B Patient and Normal Control Patient has lesion X and is impaired on A, but not B Control performs well on both A and B Lesioned area X supports A, not B Problems with logic?? Double Dissociation Two patient groups Lesion X impaired function A, not B Lesion Y impaired function B, not A Concrete example from vision Lesion to inferior temporal cortex Impaired in object recognition but not visually guided action (Visual agnosia) Lesion to posterior parietal cortex Impaired in visually guided action but not object recognition Two types of visual processing dissociated 4

5 Limitations? No random assignment into groups Small sample size Can only infer role of damaged area Impairment as a result of connection or actual region? Different strategy could mask brain region function Neuroimaging Structural Methods Functional Methods Computerized Axial Tomography (CT) Magnetic Resonance Imaging (MRI) PET and fmri Positron Emission Tomography (PET) Based on the knowledge that local changes in blood flow are correlated with changes in neural activity PET blood flow fmri activation, local changes in MR signal associated with changes in oxygen levels in blood 5

6 Limitations? Radioactive substances Experiment design constrained by decay of isotope Average images across subjects Functional MRI Sensory, Motor, or Cognitive Task Neuronal Activity Metabolic Rate Oxygen Demand Blood Flow Physiology Blood Flow overcompensates for metabolic demand Excess of oxygenated hemoglobin delivered to activated region Simple fmri Task 30 second blocks Alternate moving dots, stationary dots, and blank screen every 30 seconds Subtraction Logic Isolate cognitive process that you want to study 6

7 Z=+48 Limitations? Relation between activation and area s functional contribution is unclear How critical is area in task? Subtraction methodology Newer techniques to look at single trials Temporal resolution is limited Lots of data statistical analyses and interpretation Some Newer Methods MEG Transcranial Magnetic Stimulation (TMS) Virtual lesions Is brain study necessary? (for cognition) Why does Phelps say yes? Is brain study necessary? (for cognition) Why does Phelps say yes? Brain-computer analogy flawed Limitations on cognitive function, constrained by brain Qualified by good behavioral research Cannot have success with cog neuro approaches with basic cognitive perspective to constrain questions 7